Display plate for solar cell apparatus and method of producing display plate for solar cell apparatus

The present invention relates to, for instance, a display plate for a solar watch provided with a solar cell, a display plate for a solar cell device to be used for an electronic desk calculator provided with a solar cell, and a method of manufacturing the display plate for a solar cell device.

Conventionally, for a display plate for a solar cell device, for instance, a display plate (dial plate) for a solar watch provided with a solar cell, a light that has been received is transmitted, thereby inducing an electric power generation in a solar cell (solar battery) disposed on the bottom surface side of the display plate.

In many cases, a plastic material is conventionally used for a display plate for a solar watch requiring a transmission property of a light. More specifically, a plastic material has advantages such as obtaining a transmission property of a light, reducing a cost, and simplifying a decoration such as a painting and a printing.

In general, as shown in a plan view of FIG. 36, a solar cell that is used for a portable watch such as a wrist watch as a solar watch is formed in each of four faces (A1, A2, A3, and A4) that have been equally segmented and is disposed under a dial plate. A transmission light that has been transmitted to the dial plate is uniformly irradiated to each of the four faces (A1, A2, A3, and A4), thereby resulting in the highest electric power generation efficiency.

Consequently, it is necessary to design the dial plate that is disposed on the solar cells in such a manner that a uniform amount of lights are transmitted to each of sections corresponding to the four faces (A1, A2, A3, and A4) of the solar cells, that is to say, four faces that have been equally segmented by the 12-6 o\'clock line and the 9-3 o\'clock line.

In recent years, a photoelectric conversion efficiency of such a solar cell has been extremely high. There is provided a solar cell that can efficiently drive a portable watch even in the case in which a transmittance is 15% or 20%. Moreover, a solar cell can be miniaturized. A miniaturized solar cell of 10 mm×10 mm has been put on the market to obtain an electric power generation amount capable of driving the portable watch satisfactorily.

However, the solar cell has a generic deep violet color, and the cross lines for the segmentation into four equal divisions are extremely conspicuous due to a difference in materials. Consequently, the solar cell spoils the beauty of the portable watch. To soften the deep violet color or make the deep violet color invisible, many ideas have been carried out for the dial plate.

More specifically, the display plate must be at least semi-permeable to enable the sunlight to be transmitted. Consequently, the material of the display plate is restricted. In addition, a color tone of deep violet that is intrinsic to the solar battery is visible through the display plate, thereby disadvantageously spoiling the appearance quality of the portable watch.

Therefore, Patent document 1 (WO98-53373) proposes a display plate in which a metal thin film is formed on the surface of a resin substrate to which a light can be transmitted as a display plate for a solar watch, thereby preventing a solar cell disposed under the display plate from being visible from the outside. The display plate has a light transmittance enabling an electric power generation in the solar cell.

Moreover, Patent document 2 (WO95-27234) proposes a display plate that displays a metal quality higher than that of the display plate for the solar watch in accordance with Patent document 1. For the display plate in accordance with Patent document 2, a metal plate in which a hole is formed in a decorative section such as a number is laminated on a light transmission display plate made of a resin or the like, and a solar cell disposed under the display plate is prevented from being visible from the outside. The display plate has a light transmittance enabling an electric power generation in the solar cell and displays a metal quality sense.

Furthermore, Patent document 3 (Japanese Patent Application Laid-Open Publication No. 9-243759) proposes a display plate for a solar watch in which a solar cell is prevented from being visible from the outside. The display plate has a light transmittance enabling an electric power generation in the solar cell and has an enlarged design variation.

FIG. 37 is a partially enlarged cross-sectional view showing the structure of a display plate for a watch provided with a solar cell in accordance with an embodiment disclosed in Patent document 3.

As shown in FIG. 37, a display plate B is disposed on the surface of a solar cell 311 in an integrating manner.

In this case, the display plate B is composed of a display substrate 312, a light storage fluorescent material layer 313, and a surface protection coating layer 314 in a laminating manner. Time characters 315 are then disposed on the display plate B.

The display substrate 312 is made of a transparent resin plate such as an acrylic resin and a polycarbonate resin. The light storage fluorescent material layer 313 is made of a paint film in which a light diffusing agent and a light storage fluorescent material of a light persistent type functioning as the coloring and light diffusing agent are mixed to a binder made of a transparent resin.

In this case, silicic acid powder, calcium carbonate powder, calcium phosphate powder, or the like is used as the light diffusing agent. The light diffusing agent with a particle diameter in the range of 5 to 15 μm to be mixed is in the range of 3 to 18 weight % to the powder of the light storage fluorescent material.

The light storage fluorescent material is a long light persistent type. The light storage fluorescent material to be compounded is 100 parts by weight to the range of 35 to 65 parts by weight of the binder.

Moreover, the surface protection coating layer 314 is formed using a transparent resin such as an acrylic resin, a urethane resin, and an epoxy resin by a method such as a printing to prevent the light storage fluorescent material from being deteriorated. The time characters 315 are formed by a printing or a mounting.

By such a configuration, by an operation of the light diffusing agent and the light storage fluorescent material of a light persistent type functioning as the coloring and light diffusing agent, a reflected light from the solar cell is absorbed by the light storage fluorescent material and diffused and dispersed by the light diffusing agent. Consequently, a deep violet color of the solar cell is extinguished to prevent a color tone of the solar cell from being visible.

Moreover, by such a configuration, a color tone (white color tone) of the light storage fluorescent material can be visible from an observer.

FIG. 38 is a partially enlarged cross-sectional view showing a display plate for a watch provided with a solar cell in accordance with another embodiment disclosed in Patent document 3 (Japanese Patent Application Laid-Open Publication No. 9-243759).